Additive for nickel plating baths

ABSTRACT

ACID NICKEL PLATING BATH FOR OBTAINING BRIGHT NICKEL DEPOSITS, SAID BATH BEING OF THE CHLORIDE, SULFATE, FLUOBORATE OR SULFAMATE TYPE AND CONTAINING A BRIGHTENER MIXTURE COMPRISING THE DISODIUM SALT OF METHYLENE BIS NAPHTHALENE SULFONIC ACID AND A SECOND COMPONENT SELECTED FROM COUMARIN, PIPERONAL BISULFITE COMPLEX, SODIUM BETASTSYRENE SULFONATE, BENZIMIDAZOLE AND MIXTURES THEREOF, WITH THE PROVISO THAT BENZIMIDAZOLE IS USED ONLY WHEN GREATER THAN 50 MOLE PERCENT OF NICKEL SALT USED IN THE BATH IS NICKEL FLUOBORATE.

United States Patent 3,748,236 ADDITIVE FOR NICKEL PLATING BATHS WilliamR. Schevey, Hawley, Pa, assignor to Allied Chemical Corporation, NewYork, N.Y. No Drawing. Filed July 20, 1972, Ser. No. 273,574 Int. Cl.C23b 5/08, 5/46 U.S. Cl. 204-49 6 Claims ABSTRACT OF THE DISCLOSURE Acidnickel plating bath for obtaining bright nickel deposits, said bathbeing of the chloride, sulfate, fluoborate or su'lfamate type andcontaining a brightener mix ture comprising the disodium salt ofmethylene bis naphthalene sulfonic acid and a second component selectedfrom coumarin, piperonal bisulfite complex, sodium betastyrenesulfonate, benzimidazole and mixtures thereof, With the proviso thatbenzimidazole is used only when greater than 50 mole percent of nickelsalt used in the bath is nickel fluoborate.

BACKGROUND OF THE INVENTION Acid nickel plating baths normally yielddull electrodeposits, but bright deposits can be obtained by theaddition of effective amounts of certain organic compounds, known asbrighteners.

It is the object of this invention to provide a novel mixture ofbrighteners for use in acid nickel plating baths.

It is a further object to provide improved acid nickel bath compositionsfor bright nickel plating.

It is still another object to provide an improved method for obtainingbright nickel electrodeposits.

SUMMARY OF THE INVENTION It has been discovered that when bothBrightener A and Brightener B, defined below, are added in sufiicientamounts to a conventional acid nickel plating bath of the sulfate,chloride, fluoborate or sulfamate type, a bright nickel electrodepositis obtained which is superior to the deposit obtained when only one ofBrightener A or Brightener B is added to the bath.

The plating bath comprises an aqueous acid solution of nickel saltselected from the group consisting of nickel sulfate, nickel chloride,nickel fluoborate, nickel sulfamate or mixtures thereof.

Brightener A is the disodium salt of methylene bis naphthalene sulfonicacid and has the structural formula:

Q oH,-@ j NaOaS SOaNa wherein each SO Na group can replace any onehydrogen atom in each naphthalene group.

Brightener B is selected from the group consisting of:

(l) Coumarin, having the structural formula:

(2) Piperonal bisulfite complex, having the structural formula:

OaNa Patented July 24, 1973 (3) Sodium beta-styrene sulfonate, havingthe structural formula:

HC=OSOaNa (4) Benzimidazole, having the structural formula:

DETAILED DESCRIPTION Brightener A and Brightener B are each added to theplating both in amounts suflicient to obtain a bright nickelelectrodeposit. Generally, the concentration of Brightener A and ofBrightener B dissolved in the nickel plating bath independently rangefrom about 0.1 to about 10 grams per liter of plating bath, but notexceeding the saturation concentration thereof. Although some of thebrightener compounds have saturation concentrations greater than 10grams per liter, no advantage is seen from the use of such higherconcentration. Preferably the concentrations of Brightener A andBrightener B independently range from about 0.12 to about 2.0 grams perliter but not exceeding the saturation concentration thereof.

While Brightener A and Brightener B can each be added to the nickelplating bath separately, it is preferred that they first be premixed, sothat they can be added to the bath in one step. This mixture, called thebrightener mixture, should contain sufiicient amounts of Brightener Aand Brightener B so that when the mixture is added to the plating bath,the above-indicated bath concentrations Will be satisfied.

A convenient method of adding the brightener mixture to the plating bathis to first prepare a solution of the brightener mixture, and then addsaid solution to the plating bath. The solvent used in preparing thesolution of brightener mixture should be soluble in the plating bath.Preferably the solvent is selected from the group consisting of water,aliphatic monohydric alcohols having from 1 to 3 carbon atoms andmixtures thereof. The aliphatic monohydric alcohols are methanol,ethanol, npropanol and isopropanol, with isopropanol being preferred.When the brightener mixture includes coumarin, it is preferred that thesolvent contain at least 25 volume percent alcohol.

The ratio of Brightener A to Brightener B in the brightener mixture ordissolved in the bath is not critical, but generally the weight ratiovaries from about 0.1:1 to about 10:1, preferably from about 0.5:1 toabout 2:1.

The brightener mixtures of this invention are generally compatible withaddition agents conventionally employed in plating baths, for example,wetting agents, such as sodium lauryl sulfate and castile soap, antifoamagents, stress relief agents and the like.

It is a preferred embodiment of this invention that the brightenermixtures be used in conjunction with saccharin. Saccharin has the effectof reducing the stress and brittleness of the nickel deposit and alsosomewhat increases the brightness of the deposit. Generally, theconcentration of saccharin ranges from about 0.1 gram per liter of 3plating bath to its saturation concentration, preferably from about 0.5to about 2.0 grams per liter of plating bath.

Saccharin may be added to the bath separately or it may first beincorporated as part of the brightener mixture. In the latter case, theamount of saccharin in the brightener mixture is not critical as long asthe amount is sufiicient to supply the above indicated concentrations ofsaccharin in the bath. Generally, the weight ratio of saccharin tobrightener mixture varies from about 0.1:1 to about :1, preferably fromabout 1:1 to about 8:1.

The bright nickel deposit is obtained in conventional manner by passinga current through a nickel plating bath containing Brightener A andBrightener B, between the anode, which is typically nickel, and thecathode, which is the article to be plated.

Temperature, current density, pH, and other operating conditions arerelevant only as far as they influence the basic characteristics of theplating bath in known manner. Thus operating conditions commonlyemployed with the conventional nickel plating solutions may be employedwhen those solutions contain the brightener mixtures.

Generally, plating bath temperatures may vary from about 40 to about 170F., preferably from about 90 to about 140 F.

Current density generally ranges from about 1 to about 300 amps persquare foot, preferably from about 10 to about 150 amps per square foot.For plating of wires, current densities as high as 600 amps per squarefoot can be employed. With Watts nickel type baths,'however, lowercurrent densities are generally employed, usually up to about 80 ampsper square foot, with up to about 100 amps per square foot for wires.

Values for bath pH generally range from about 2.5 to about 5.0,preferably from about 3.5 to about 4.5. A bath pH between about 5.0 andabout 7.0 can also be employed, but at these pH values, the bath usuallyrequires the addition of nickel complexing agents, e.g. citric acid,malic acid or ammonium hydroxide.

It is preferred that during the plating process relative movement beprovided between the plating bath and the object being plated. Anyconventional means for agitating the bath or for moving the object beingplated may be employed. Illustrative of such means are mechanicalstirring of the bath, passage of compressed air through the bath,cathode rod agitation, and the like.

The baths listed in the following table illustrate, but do not limit,the types of electroplating baths in which the brightener mixtures ofthis invention may be incorporated as addition agents in the aboveindicated proportions. The composition ranges generally employed in theart are stated for each of the baths in grams per liter of bath.

The above nickel baths generally may contain minor amounts of othernickel salts. For example, the above fluoborate bath may additionallycontain nickel chloride or nickel sulfate, usually in such amounts thatat least about mole percent of the nickel salt is nickel fluoborate.

The preferred bath is a nickel fiuoborate bath wherein the nickelfluoborate concentration ranges from about 220 to 440 grams per liter,especially wherein at least about 80 mole percent of the nickel salt isnickel fluoborate.

The invention can be more fully understood by reference to the followingexamples.

EXAMPLE 1 Tests were carried out in a heated 267 ml. Hull Cell, platingonto brass Hull Cell panels. All samples were compared at one to twoamps. The plating solution was a nickel fluoborate solution having thefollowing characteristics:

Ni(B F 440 grams/liter. pH 4.

Temperature F.

Runs were made both with and without air agitation of the solutions.

The various brighteners used and descriptions of the resultant platesare listed in Table 11 'below. In Table II the units g./1. refer tograms of brightener per liter of plating bath. The term Tamol N is atrademark for a mixture of disodium salts of methylene bis naphthalenesulfonic acid. The term Heloplex is a trademark for piperonal bisulfitecomplex.

TABLE II Brightener Plate description 1 Blank Dull. 1A Blank, plusagitation Do. 2 .15 g./1. Tamol N. Brighgtbelow 20 amps] S 2A .15 g./l.Tamol N, plus agitation Do. 3- .15 g./l. Tamol N, 1.0 g./l. saccharin.Semi-bright. 3A.... .15 g./l. Tamol N, 1.0 gJl. saceharin, 0.

plus agitation. 4 .15 g./l. coumarin Dull. 411."- .15 g./l. cournarin,plus agitation. Dull with bright spots. 5 .15 g./l. coumarin, .15 g./l.Tamol N Brimght liiwith gas bubble S rea 5. 5A .15 gJi. coumarin, .15g./l. Tamol N, Bright.

plus agitation. 6-.. .15 g./i. coumarin, .15 g./l. Taanol N, Bright, butpitted.

1.0 g./l. saccharin. 6A.-.. .15 g./l. coumarin, .15 g./l. Ta-mol N,Bright.

1.0 gjl. saceharin, plus agitation. 7 c .15 g.ll. benzimidazole Dullwith bright spots. 7A..-. .15 g./l. benzimidazole, plus agitation Do.8-.." .15g1./l. Tamol N, .15 g./l. benzimida- Bright.

Z0 8. 8A.... .15 gJl. Tamol N, .15 g./l. benzimida- Do.

2016, plus agitation. 9..-.. 15 g./l. Tamol N, .15 gJl. benzim1da-Bright, put pitted.

zole, 1.0 g./l. saceharin. 9A--.. .15 g./l. Tamol N, .15 gJl. benzimida-Bright. zgle, 1.0 g./l. saccharin, plus agitaion. 10. .15 g./l. sodiumbeta-styrene sulionate. Semi-bright. 10A... .15 g./l. sodiumbeta-styrene sulfonate, Do.

plus agitation. 11 .15 g./l. Tamol N, .15 g./l. sodium beta- Semi-bright(but styrene sulfonate. brighter than run 10). 11A... .15 g./l. Tamol N,.15 g./l. sodium beta Bright.

styrene sulionate, plus agitation. 12-..; .15g./l. Tamol N, .15g./l.sodium beta- Do. styrene sulfonate, 1.0 g./1. saccharin. 12A .15 g./l.Tamol N, .15 g./1. sodium beta- Do. styrene sulfonate, 1.0 g./l.saceharin, plus agitation. 13-..: .15 g./l. Heloplex Dull, bright streakat 12 amps/sq. ft. 13A... .15 g./l. Heloplex, plus agitation- Dull withbright streak. 14. .15 g./l. Tamol N, .15 g./l. Heloplex Bright, butpitted. 1 .15 g./l. Tamol N, .15 g./1. Heloplex, Bright.

plus agitation. 15...; .15 g./l. Tarnol N, .15 gJl. Heloplex, Do.

1.0 g./1. saceharin. 15A... .15 g.ll. Tamol N, .15 g./l. Heloplex, Do.

1.0 g./l. saceharin,1p1us agitation. 16 .15 g./l. eonmarin, .15 g./lIsodium beta- Dull.

styrene sulfonate. 16A .15 g./l. eoumarin, .15g.ll.1s0dium betar Dullwith brights spots.

styrene sulionate, plus agitation. 17-..: :15 g./l. Heloplex, .15 g./l.coumarin- Do. 18---- .15 g./l. Heloplex, .15 g./l.1eoumarin, Do.

1.0 g.[l. sacoharin. 19.-.- .15 g./l. Heloplex, .15 g./l. benzimida-Bright streaks.

zole. 20- .15 g.ll. Heloplex, .15 g./1. benzimida- Dull with brightspots.

zole, 1.0 g./l. saecharin. 20A-.. :15 g./l. Heloplex, .15 g./l.benzunidw Do.

min, 1.0 g./l saccharin, plus agitation.

Example 2 The tests of Example 1 are repeated using a Watts Nickel typebath having the following characteristics:

NiSO 6H O grams/liter 300 NiCl 6H O do 45 Boric acid do 30 P 4Temperature F 110 Results substantially similar to those of Example 1are obtained, except that no brightening is observed when brightenermixtures containing benzimidazole are used.

Example 3 The tests of Example 1 are repeated using a nickel sulfamatebath having the following characteristics:

Ni(NH SO grams/liter 300 Boric acid do 30 pH 4 Temperature F 110 2. Thebrightener mixture of claim 1 wherein the weight ratio of Brightener Ato Brightener B varies from about 0.121 to about 10:1.

3. The brightener mixture of claim 1 wherein the weight ratio ofBrightener A to Brightener B various from about 0.5:1 to about 2:1.

4. The brightener mixture of claim 3 which additionally containssaccharin.

5. A solution of the brightener mixture of claim 2 in water, aliphaticmonohydric alcohols having from 1 to 3 carbon atoms, or mixturesthereof.

6. A solution of the brightener mixture of claim 1 in water, aliphaticmonohydric alcohols having from 1 to 3 carbon atoms, or mixturesthereof.

References Cited UNITED STATES PATENTS 2,774,728 12/ 1956 .Wernlund20452 Y 2,841,542 7/1958 Manquen 20452 Y 2,854,389 9/1958 Boelter, Jr.20452 Y 2,885,331 5/1959 McLeod et a1 20452 Y 2,970,951 2/ 1961 Manquenet a1. 20452 Y 3,296,101 1/19'67 Crain 20452 Y 3,661,731 5/ 1972 Schevey20449 GERALD L. KAPLAN, Primary Examiner US. Cl. X.R. 204-DIG 2

